In the Tot 1.0.3 for macOS release, a theme editor was added:
 

• Use Option key in Tot menu or Cmd-Option-, to open Theme Preferences
• Select the dot you want to change in the main window
• Changes to color well are displayed immediately
• New colors are synced to all devices, including iOS
• Share your theme as .tot file with save/load in Theme Preferences
• Theme file is JSON with hex colors: easy to modify in text editor, too